Chiller system with serial flow evaporators

ABSTRACT

A heating, ventilation, air conditioning, and/or refrigeration (HVAC&amp;R) system includes a first refrigerant circuit having a first evaporator configured to place a first refrigerant in a heat exchange relationship with a conditioning fluid, where the first evaporator includes a first set of first tubes and a second set of first tubes configured to direct the conditioning fluid through the first evaporator. The HVAC&amp;R system also includes a second refrigerant circuit having a second evaporator configured to place a second refrigerant in a heat exchange relationship with the conditioning fluid, where the second evaporator includes a first set of second tubes and a second set of second tubes configured to direct the conditioning fluid through the second evaporator. The HVAC&amp;R system further includes a conditioning fluid circuit configured to circulate the conditioning fluid serially through the first set of first tubes, the second set of first tubes, the first set of second tubes, and the second set of second tubes.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described below. This discussion is believed to be helpful inproviding the reader with background information to facilitate a betterunderstanding of the various aspects of the present disclosure.Accordingly, it should be noted that these statements are to be read inthis light, and not as admissions of prior art.

Chiller systems, or vapor compression systems, utilize a working fluid(e.g., a refrigerant) that changes phases between vapor, liquid, andcombinations thereof, in response to exposure to different temperaturesand pressures within components of the chiller system. A chiller systemmay place the working fluid in a heat exchange relationship with aconditioning fluid (e.g., water) and may deliver the conditioning fluidto conditioning equipment and/or a conditioned environment serviced bythe chiller system. In such applications, the conditioning fluid may bepassed through downstream equipment, such as air handlers, to conditionother fluids, such as air in a building.

Traditional chiller systems include a refrigerant circuit including, forexample, a compressor, a condenser, and an evaporator. In someinstances, a chiller system may include multiple refrigerant circuits,and each refrigerant circuit includes a respective compressor,condenser, and evaporator. The multiple refrigerant circuits may operateseparately or in conjunction with one another to condition theconditioning fluid for delivery to the conditioning equipment.Unfortunately, existing chiller systems having multiple refrigerantcircuits may be arranged in configurations that limit the performanceand/or efficiency of the chiller system.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below. Itshould be noted that these aspects are presented merely to provide thereader with a brief summary of these certain embodiments and that theseaspects are not intended to limit the scope of this disclosure. Indeed,this disclosure may encompass a variety of aspects that may not be setforth below.

In an embodiment, a heating, ventilation, air conditioning, and/orrefrigeration (HVAC&R) system includes a first refrigerant circuithaving a first evaporator configured to place a first refrigerant in aheat exchange relationship with a conditioning fluid, where the firstevaporator includes a first set of first tubes and a second set of firsttubes configured to direct the conditioning fluid through the firstevaporator. The HVAC&R system also includes a second refrigerant circuithaving a second evaporator configured to place a second refrigerant in aheat exchange relationship with the conditioning fluid, where the secondevaporator includes a first set of second tubes and a second set ofsecond tubes configured to direct the conditioning fluid through thesecond evaporator. The HVAC&R system further includes a conditioningfluid circuit configured to circulate the conditioning fluid seriallythrough the first set of first tubes, the second set of first tubes, thefirst set of second tubes, and the second set of second tubes.

In an embodiment, a heating, ventilation, air conditioning, and/orrefrigeration (HVAC&R) system includes a first evaporator having a firstlower tube bundle and a first upper tube bundle, where the first lowertube bundle and the first upper tube bundle are each configured to placea conditioning fluid in a heat exchange relationship with a firstrefrigerant, and a second evaporator having a second lower tube bundleand a second upper tube bundle, where the second lower tube bundle andthe second upper tube bundle are each configured to place theconditioning fluid in a heat exchange relationship with a secondrefrigerant. The HVAC&R system also includes a conduit fluidly extendingbetween the first evaporator and the second evaporator and fluidlycoupling the first lower tube bundle and the second upper tube bundleand includes a conditioning fluid circuit configured to circulate theconditioning fluid serially through the second lower tube bundle, thesecond upper tube bundle, the conduit, the first lower tube bundle, andthe first upper tube bundle.

In an embodiment, a chiller system includes a first refrigerant circuithaving a first evaporator configured to place a first refrigerant in aheat exchange relationship with a conditioning fluid, where the firstevaporator includes a first plurality of first tubes and a secondplurality of first tubes configured to direct the conditioning fluidthrough the first evaporator, the first plurality of first tubes definesa lower pass of the first evaporator, and the second plurality of firsttubes defines an upper pass of the first evaporator. The chiller systemalso includes a second refrigerant circuit having a second evaporatorconfigured to place a second refrigerant in a heat exchange relationshipwith the conditioning fluid, where the second evaporator includes afirst plurality of second tubes and a second plurality of second tubesconfigured to direct the conditioning fluid through the secondevaporator, where the first plurality of second tubes defines a lowerpass of the second evaporator, and the second plurality of second tubesdefines an upper pass of the second evaporator. The chiller systemfurther includes a conduit fluidly coupled between the second pluralityof second tubes and the first plurality of first tubes.

DRAWINGS

Various aspects of this disclosure may be better understood upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a perspective view of a building that may utilize anembodiment of a heating, ventilation, air conditioning, and/orrefrigeration (HVAC&R) system in a commercial setting, in accordancewith an aspect of the present disclosure;

FIG. 2 is a schematic of an embodiment of a vapor compression system, inaccordance with an aspect of the present disclosure;

FIG. 3 is a schematic of an embodiment of an HVAC&R system havingmultiple refrigerant circuits, illustrating evaporators of the multiplerefrigerant circuits in a serial flow arrangement, in accordance with anaspect of the present disclosure;

FIG. 4 is a side view of an embodiment of evaporators of multiplerefrigerant circuits in a serial flow arrangement, illustrating theevaporators in an aligned configuration, in accordance with an aspect ofthe present disclosure;

FIG. 5 is a top view of an embodiment of evaporators of multiplerefrigerant circuits in a serial flow arrangement, illustrating theevaporators in a side-by-side configuration, in accordance with anaspect of the present disclosure;

FIG. 6 is an axial view of an embodiment of evaporators of multiplerefrigerant circuits in a serial flow arrangement, illustrating theevaporators in a side-by-side configuration, in accordance with anaspect of the present disclosure; and

FIG. 7 is a schematic of an embodiment of an HVAC&R system havingmultiple refrigerant circuits, illustrating a control system andevaporators of the multiple refrigerant circuits in a serial flowarrangement, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, not all featuresof an actual implementation are described in the specification. Itshould be noted that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be noted that such a development effortmight be complex and time consuming, but would nevertheless be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be noted that references to “one embodiment” or“an embodiment” of the present disclosure are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features.

Embodiments of the present disclosure relate to a heating, ventilation,air conditioning, and/or refrigeration (HVAC&R) system, such as achiller system. The HVAC&R system may include a vapor compression systemthrough which a refrigerant is directed in order to heat and/or cool aconditioning fluid. As an example, the vapor compression system mayinclude a compressor configured to pressurize the refrigerant and todirect the pressurized refrigerant to a condenser configured to cool thepressurized refrigerant. An evaporator of the vapor compression systemmay receive the cooled refrigerant and may place the cooled refrigerantin a heat exchange relationship with the conditioning fluid to absorbthermal energy or heat from the conditioning fluid, thereby cooling theconditioning fluid. The cooled conditioning fluid may then be directedto conditioning equipment, such as air handlers and/or terminal units,for use in conditioning air supplied to a building or other conditionedspace.

Is some embodiments, the vapor compression system may include multiplerefrigerant circuits with each refrigerant circuit including arespective condenser, compressor, and evaporator. For example, theevaporators of the multiple refrigerant circuits may cooperatively coolthe conditioning fluid for use with the conditioning equipment. In otherwords, the evaporators may operate to cool a common flow of theconditioning fluid. Some evaporators are configured to cool theconditioning fluid via tubes that form a flow path defining multiplepasses through the evaporator. For example, in a two-pass evaporator,the conditioning fluid may be directed through a first tube bundle ofthe evaporator in a first direction, and the flow of the conditioningfluid may be reversed (e.g., via a water box of the evaporator) and thendirected through a second tube bundle of the evaporator in a seconddirection opposite the first direction.

Existing systems having multiple (e.g., two) refrigerant circuitstypically include evaporators packaged together and configured to coolconditioning fluid by directing the conditioning fluid alternatinglybetween the evaporators. For example, existing systems may directconditioning fluid sequentially through a first (e.g., lower) tubebundle or pass of a first evaporator and then through a first (e.g.,lower) tube bundle or pass of the second evaporator. Thereafter, theflow direction of the conditioning fluid may be reversed, and theconditioning fluid may be directed sequentially through a second (e.g.,upper) tube bundle or pass of the second evaporator and then through asecond (e.g., upper) tube bundle or pass of the first evaporator.Unfortunately, the configurations of existing systems may result inhigher evaporator approach temperatures than desired, which may resultin reduced heat transfer between refrigerant and conditioning fluid,higher energy consumption (e.g., of compressors of the multiplerefrigerant circuits), and/or reduced capacity of the multiplerefrigerant circuits.

Thus, it is presently recognized that there is a need to improve theoperation of HVAC systems having multiple refrigerant circuits byreducing the evaporator approach temperature(s) of the HVAC&R system. Inthis way, refrigerant pressure in the evaporators may be raised, whichmay reduce a lift (e.g., difference between condenser refrigerantpressure and evaporator refrigerant pressure) of the HVAC&R system andtherefore reduce the work performed by compressors of the HVAC&R system.Accordingly, energy consumption of the HVAC&R system is reduced. Inorder to achieve a reduction in evaporator approach temperature, theevaporators of the multiple refrigerant circuits may be arranged in aserial flow arrangement. As used herein, “serial flow” refers to flow ofconditioning fluid first through the passes of one evaporator of theHVAC&R system and subsequently through the passes of another evaporatorof the HVAC&R system. In other words, the conditioning fluid receivedfrom the conditioning equipment first flows through a first evaporatorof the HVAC&R system, then flows through a second evaporator of theHVAC&R system, and is then directed back to the conditioning equipment.As discussed in detail below, the serial flow arrangement of theevaporators in a multiple refrigerant circuit system enables efficiencyimprovements and reductions in costs associated with the HVAC&R system.

Turning now to the drawings, FIG. 1 is a perspective view of anembodiment of an application for a heating, ventilation, airconditioning, and/or refrigeration (HVAC&R) system. Such systems, ingeneral, may be applied in a range of settings, both within the HVAC&Rfield and outside of that field. The HVAC&R systems may provide coolingto data centers, electrical devices, freezers, coolers, or otherenvironments through vapor compression refrigeration, absorptionrefrigeration, or thermoelectric cooling. In presently contemplatedapplications, however, HVAC&R systems may be used in residential,commercial, light industrial, industrial, and in any other applicationfor heating or cooling a volume or enclosure, such as a residence,building, structure, and so forth. Moreover, the HVAC&R systems may beused in industrial applications, where appropriate, for basic coolingand heating of various fluids.

The illustrated embodiment shows an HVAC&R system for buildingenvironmental management that may utilize heat exchangers. A building 10is cooled by a system that includes a chiller 12 and a boiler 14. Asshown, the chiller 12 is disposed on the roof of building 10, and theboiler 14 is located in the basement; however, the chiller 12 and boiler14 may be located in other equipment rooms or areas next to the building10. The chiller 12 may be an air cooled or water cooled device thatimplements a refrigeration cycle to cool water or other conditioningfluid. The chiller 12 is housed within a structure that may include oneor more refrigeration circuits, a free cooling system, and associatedequipment such as pumps, valves, and piping. For example, the chiller 12may be single package rooftop unit. The boiler 14 is a closed vessel inwhich water is heated. The water from the chiller 12 and the boiler 14is circulated through the building 10 by water conduits 16. The waterconduits 16 are routed to air handlers 18 (e.g., conditioning equipment)located on individual floors and within sections of the building 10.

The air handlers 18 are coupled to ductwork 20 that is adapted todistribute air between the air handlers 18 and may receive air from anoutside intake (not shown). The air handlers 18 include heat exchangersthat circulate cold water from the chiller 12 and hot water from theboiler 14 to provide heated or cooled air to conditioned spaces withinthe building 10. Fans within the air handlers 18 draw air through theheat exchangers and direct the conditioned air to environments withinbuilding 10, such as rooms, apartments, or offices, to maintain theenvironments at a designated temperature. A control device, shown hereas including a thermostat 22, may be used to designate the temperatureof the conditioned air. The control device 22 also may be used tocontrol the flow of air through and from the air handlers 18. Otherdevices may be included in the system, such as control valves thatregulate the flow of water and pressure and/or temperature transducersor switches that sense the temperatures and pressures of the water, theair, and so forth. Moreover, control devices may include computersystems that are integrated with or separate from other building controlor monitoring systems, and even systems that are remote from thebuilding 10.

FIG. 2 is a schematic of an embodiment of a vapor compression system 30of an HVAC&R system that includes a refrigerant circuit 34 configured tocool a conditioning fluid (e.g., water). For example, the vaporcompression system 30 may be a part of an air-cooled chiller. However,it should be noted that the disclosed techniques may be incorporatedwith a variety of other types of chillers, such as water-cooledchillers. The refrigerant circuit 34 is configured to circulate aworking fluid, such as refrigerant, therethrough with a compressor 36(e.g., a screw compressor) disposed along the refrigerant circuit 34.The refrigerant circuit 34 also includes the flash tank 32, a condenser38, expansion valves or devices 40, and a liquid chiller or anevaporator 42. The components of the refrigerant circuit 34 enable heattransfer between the working fluid and other fluids (e.g., aconditioning fluid, air, water, etc.) in order to provide cooling to anenvironment, such as an interior of the building 10.

Some examples of working fluids that may be used as refrigerants in thevapor compression system 30 are hydrofluorocarbon (HFC) basedrefrigerants, for example, R-410A, R-407, R-134a, hydrofluoro-olefin(HFO), “natural” refrigerants like ammonia (NH3), R-717, carbon dioxide(CO2), R-744, or hydrocarbon based refrigerants, water vapor,refrigerants with low global warming potential (GWP), or any othersuitable refrigerant. In some embodiments, the vapor compression system30 may be configured to efficiently utilize refrigerants having a normalboiling point of about 19 degrees Celsius (66 degrees Fahrenheit orless) at one atmosphere of pressure, also referred to as low pressurerefrigerants, versus a medium pressure refrigerant, such as R-134a. Asused herein, “normal boiling point” may refer to a boiling pointtemperature measured at one atmosphere of pressure.

The vapor compression system 30 may further include a control panel 44(e.g., controller) that has an analog to digital (A/D) converter 46, amicroprocessor 48, a non-volatile memory 50, and/or an interface board52. In some embodiments, the vapor compression system 30 may use one ormore of a variable speed drive (VSDs) 54 and a motor 56. The motor 56may drive the compressor 36 and may be powered by the VSD 54. The VSD 54receives alternating current (AC) power having a particular fixed linevoltage and fixed line frequency from an AC power source, and providespower having a variable voltage and frequency to the motor 56. In otherembodiments, the motor 56 may be powered directly from an AC or directcurrent (DC) power source. The motor 56 may include any type of electricmotor that can be powered by the VSD 54 or directly from an AC or DCpower source, such as a switched reluctance motor, an induction motor,an electronically commutated permanent magnet motor, or another suitablemotor.

The compressor 36 compresses a refrigerant vapor and may deliver thevapor to an oil separator 58 that separates oil from the refrigerantvapor. The refrigerant vapor is then directed toward the condenser 38,and the oil is returned to the compressor 36. The refrigerant vapordelivered to the condenser 38 may transfer heat to a cooling fluid atthe condenser 38. For example, the cooling fluid may be ambient air 60forced across heat exchanger coils of the condenser 38 by condenser fans62. The refrigerant vapor may condense to a refrigerant liquid in thecondenser 38 as a result of thermal heat transfer with the cooling fluid(e.g., the ambient air 60).

The liquid refrigerant exits the condenser 38 and then flows through afirst expansion device 64 (e.g., expansion device 40, electronicexpansion valve, etc.). The first expansion device 64 may be a flashtank feed valve configured to control flow of the liquid refrigerant tothe flash tank 32. The first expansion device 64 is also configured tolower the pressure of (e.g., expand) the liquid refrigerant receivedfrom the condenser 38. During the expansion process, a portion of theliquid may vaporize, and thus, the flash tank 32 may be used to separatethe vapor from the liquid received from the first expansion device 64.Additionally, the flash tank 32 may provide for further expansion of theliquid refrigerant due to a pressure drop experienced by the liquidrefrigerant when entering the flash tank 32 (e.g., due to a rapidincrease in volume experienced upon entering the flash tank 32).

The vapor in the flash tank 32 may exit and flow to the compressor 36.For example, the vapor may be drawn to an intermediate stage ordischarge stage of the compressor 36 (e.g., not a suction stage). Avalve 66 (e.g., economizer valve, solenoid valve, etc.) may be includedin the refrigerant circuit 34 to control flow of the vapor refrigerantfrom the flash tank 32 to the compressor 36. In some embodiments, whenthe valve 66 is open (e.g., fully open), additional liquid refrigerantwithin the flash tank 32 may vaporize and provide additional subcoolingof the liquid refrigerant within the flash tank 32. The liquidrefrigerant that collects in the flash tank 32 may be at a lowerenthalpy than the liquid refrigerant exiting the condenser 38 because ofthe expansion in the first expansion device 64 and/or the flash tank 32.The liquid refrigerant may flow from the flash tank 32, through a secondexpansion device 68 (e.g., expansion device 40, an orifice, etc.), andto the evaporator 42. In some embodiments, the refrigerant circuit 34may also include a valve 70 (e.g., drain valve) configured to regulateflow of liquid refrigerant from the flash tank 32 to the evaporator 42.For example, the valve 70 may be controlled (e.g., via the control panel44) based on an amount of suction superheat of the refrigerant.

The liquid refrigerant delivered to the evaporator 42 may absorb heatfrom a conditioning fluid, which may or may not be the same coolingfluid used in the condenser 38. The liquid refrigerant in the evaporator42 may undergo a phase change to become vapor refrigerant. For example,the evaporator 42 may include one or more tube bundles fluidly coupledto a supply line 72 and a return line 74 that are connected to a coolingload. The conditioning fluid of the evaporator 42 (e.g., water, oil,calcium chloride brine, sodium chloride brine, or any other suitablefluid) enters the evaporator 42 via the return line 74 and exits theevaporator 42 the via supply line 72. The evaporator 42 may reduce thetemperature of the conditioning fluid in the tube bundle via thermalheat transfer with the refrigerant so that the conditioning fluid may beutilized to provide cooling for a conditioned environment. The tubebundle in the evaporator 42 can include a plurality of tubes and/or aplurality of tube bundles. In some embodiments, the tubes or tubebundles may define multiple passes through the evaporator 42. In anycase, the refrigerant vapor exits the evaporator 42 and returns to thecompressor 36 by a suction line to complete the refrigerant cycle.

In some circumstances, an HVAC&R system may include multiple refrigerantcircuits configured to separately and/or cooperatively cool theconditioning fluid. As disclosed herein, present embodiments include anHVAC&R system having multiple refrigerant circuits in which theevaporators of the multiple refrigerant circuits are arranged in aserial flow arrangement (e.g., relative to a flow of conditioning fluidthrough the evaporators). In other words, the evaporators are arranged,fluidly coupled, and/or packaged such that the conditioning fluidreceived from the cooling load first flows through one evaporator of onerefrigerant circuit, then flows through another evaporator of anotherrefrigerant circuit, and is then directed back to the cooling load. Forexample, the conditioning fluid may first be sequentially directedthrough multiple passes of one evaporator and subsequently besequentially directed through multiple passes of another evaporator. Inthis way, the evaporator approach temperature(s) of the HVAC&R systemmay be reduced, which results in efficiency improvements and reductionsin costs associated with the HVAC&R system.

With this in mind, FIG. 3 is a schematic of an embodiment of an HVAC&Rsystem 100 having multiple refrigerant circuits 34. More specifically,the HVAC&R system 100 includes a first refrigerant circuit 102 (e.g.,vapor compression circuit) having a first compressor 104, a firstcondenser 106, a first expansion device 108, and a first evaporator 110and includes a second refrigerant circuit 112 (e.g., vapor compressioncircuit) having a second compressor 114, a second condenser 116, asecond expansion device 118, and a second evaporator 120. Each of therefrigerant circuits 34 is configured to circulate a respectiverefrigerant therethrough and is configured to operate in a mannersimilar to that described above with reference to the refrigerantcircuit 34 shown in FIG. 2 . It should be noted that each of therefrigerant circuits 34 may also include components in addition to thoseshown in FIG. 3 , such as one or more components illustrated in therefrigerant circuit 34 of FIG. 2 . In some embodiments, the first andsecond refrigerant circuits 102 and 112 may be packaged together in asingle package unit (e.g., a rooftop unit).

As mentioned above, the first and second evaporators 110 and 120 of theHVAC&R system 100 are arranged in a serial flow arrangement.Specifically, the first and second evaporators 110 and 120 areconfigured to define a portion of a conditioning fluid flow path orcircuit 124 that extends from a cooling load 122 (e.g., air handlers118), sequentially through evaporators 110 and 120, and back to thecooling load 122. As described in further detail below, each of thefirst and second evaporators 110 and 120 may include multiple passes(e.g., tube passes, tube bundles, sets of tubes, etc.) configured todirect conditioning fluid therethrough. In accordance with the serialflow arrangement, the HVAC&R system 100 is configured to directconditioning fluid received from the cooling load 122 first through thepasses of one evaporator and subsequently through the passes of anotherevaporator before directing the conditioning fluid back to the coolingload 122. For example, in the illustrated embodiment, the HVAC&R system100 (e.g., the conditioning fluid circuit 124) is configured to directconditioning fluid first through the second evaporator 120, then throughthe first evaporator 110, before directing the conditioning fluid backto the cooling load 122. However, in other embodiments, the HVAC&Rsystem 100 may be configured to direct the conditioning fluid throughthe first evaporator 110, then through the second evaporator 120, beforedirecting the conditioning fluid back to the cooling load 122. Thedisclosed serial flow arrangement enables a reduction in the separateand/or combined evaporator approach temperature of the first evaporator110 and/or the second evaporator 120. Thus, the refrigerant pressurewithin the first evaporator 110 and/or the second evaporator 120 may beraised, which may reduce a lift of the first refrigerant circuit 102and/or the second refrigerant circuit 112, respectively. Accordingly,energy consumption of the first compressor 104 and/or the secondcompressor 114 may be reduced, which enables a reduction in costsassociated with operating the HVAC system 100.

FIG. 4 is a side view of an embodiment of the first evaporator 110 andthe second evaporator 120 of the HVAC&R system 100 connected in a serialflow arrangement 150 with respect to flow of conditioning fluidtherethrough. More specifically, the first evaporator 110 and the secondevaporator 120 are positioned in an aligned configuration (e.g., alignedalong longitudinal axes of the first evaporator 110 and the secondevaporator 120). The configuration shown in FIG. 4 may also be referredto as an end-to-end arrangement. Further, while the serial flowarrangement 150 disclosed herein is described with reference to animplementation with the first evaporator 110 and the second evaporator120, in other embodiments the serial flow arrangement 150 may beutilized with other types of heat exchangers, such as condensers, and/orwith other numbers of heat exchangers.

In the illustrated configuration, the HVAC&R system 100 (e.g., theconditioning fluid circuit 124) is configured to direct a conditioningfluid from the cooling load 122 first through the second evaporator 120,then through the first evaporator 110, and then back to the cooling load122. The first and second evaporators 110 and 120 are each configured astwo-pass heat exchangers. That is, the first evaporator 110 includes afirst pass 152 and a second pass 154, and the second evaporator 120include a first pass 156 and a second pass 158. Each of the passes 152,154, 156, and 158 may be defined by a respective set of tubes (e.g., arespective tube bundle) configured to direct the conditioning fluidtherethrough.

In each of the first and second evaporators 110 and 120, heat isexchanged between the conditioning fluid and a respective refrigerantdirected through the first and second evaporators 110 and 120. That is,a first refrigerant flowing through the first refrigerant circuit 102,as indicated by arrow 160, may be directed into a shell 162 of the firstevaporator 110, and heat may be transferred from the first refrigerant160 to the conditioning fluid flowing through the tubes of the first andsecond passes 152 and 154 of the first evaporator 110. Similarly, asecond refrigerant directed through the second refrigerant circuit 112,as indicated by arrow 164, may be directed into a shell 166 of thesecond evaporator 120, and heat may be transferred from the secondrefrigerant 164 to the conditioning fluid flowing through the tubes ofthe first and second passes 156 and 158 of the second evaporator 120. Insome embodiments, the first evaporator 110 and/or the second evaporator120 may be configured as a flooded evaporator, while in otherembodiments the first evaporator 110 and/or the second evaporator 120may be configured as a falling film evaporator.

In the illustrated embodiment, the serial flow arrangement 150 of thefirst evaporator 110 and the second evaporator 120 receives theconditioning fluid, represented by arrow 168, via an inlet 170 of thesecond evaporator 120. That is, conditioning fluid from the cooling load122 is directed into the serial flow arrangement 150 via the inlet 170.The inlet 170 directs the conditioning fluid into a first water box 172of the second evaporator 120. The first water box 172 is divided into afirst section 174 and a second section 176 by a baffle 178 that enablesfluid separation of the first section 174 and the second section 176.From the first section 174 of the first water box 172, the conditioningfluid is directed through a first tube bundle 180 (e.g., a set of tubes)defining the first tube pass 156 of the second evaporator 120, asindicated by arrow 182. In the illustrated embodiment, the first tubepass 156 is a lower tube pass of the second evaporator 120, but in otherembodiments the first tube pass 156 may be an upper tube pass or anintermediate tube pass.

From the first tube pass 156, the conditioning fluid is directed into asecond water box 184 of the second evaporator 120. The second water box184 reverses the flow direction of conditioning fluid through the secondevaporator 120, as indicated by arrow 186, to direct the conditioningfluid through the second pass 158 of the second evaporator 120.Specifically, the conditioning fluid is directed through a second tubebundle 188 (e.g., a set of tubes) of the second pass 158, as indicatedby arrow 190, which is an upper pass of the second evaporator 120. Theconditioning fluid is then directed into the second section 176 of thefirst water box 172, from which the condition fluid is discharged fromthe second evaporator 120 via an outlet 192 of the second evaporator120.

After the conditioning fluid is circulated through the second evaporator120, the conditioning fluid is then circulated through the firstevaporator 110. Specifically, as indicated by arrow 193, theconditioning fluid is directed from the second evaporator 120 to thefirst evaporator 110 via a conduit (e.g., transfer conduit) 194 thatfluidly couples the outlet 192 of the second evaporator 120 with aninlet 196 of the first evaporator 110. The first evaporator 110 has asimilar construction and/or configuration as the second evaporator 120,and the conditioning fluid is directed through the first evaporator 110in a manner similar to that described above with reference to the secondevaporator 120. For example, the inlet 196 of the first evaporator 110directs the conditioning fluid into a first water box 198 of the firstevaporator 110. The first water box 198 is divided into a first section200 and a second section 202 by a baffle 204 that enables fluidseparation of the first section 200 and the second section 202. From thefirst section 200 of the first water box 198, the conditioning fluid isdirected through a first tube bundle 206 defining the first tube pass152 of the first evaporator 110, as indicated by arrow 208. In theillustrated embodiment, the first tube pass 152 is a lower tube pass ofthe first evaporator 110, but in other embodiments the first tube pass152 may be an upper tube pass or an intermediate tube pass.

From the first tube pass 152, the conditioning fluid is directed into asecond water box 210 of the first evaporator 110. The second water box210 reverses the flow of conditioning fluid through the first evaporator110, as indicated by arrow 212, to direct the conditioning fluid throughthe second pass 154 of the first evaporator 110. Specifically, theconditioning fluid is directed through a second tube bundle 214 of thesecond pass 154, as indicated by arrow 216, which is an upper pass ofthe first evaporator 110. The conditioning fluid is then directed intothe second section 202 of the first water box 198, from which theconditioning fluid is discharged from the first evaporator 110 via anoutlet 218 of the first evaporator 110, as indicated by arrow 220.Thereafter, the conditioning fluid is directed back to the cooling load122 for use in conditioning air or another fluid.

As mentioned above, the serial flow arrangement 150 of the firstevaporator 110 and the second evaporator 120 enables a reduction in theevaporator approach temperature(s) of the first evaporator 110 and/orthe second evaporator 120. As will be appreciated, respectivetemperature differences of the entering and exiting conditioning fluidfor each of the first and second evaporators 110 and 120 may also bereduced. For example, a difference between the temperature of theconditioning fluid leaving the second evaporator 120 via the outlet 192and a saturated evaporating temperature of the second refrigerant 164may be less than that of the existing systems described above. As aresult, a pressure of the second refrigerant 164 exiting the secondevaporator 120, and therefore a suction pressure of the secondrefrigerant 164, may be greater than that of existing systems, whichenables a reduced energy consumption of the second compressor 114.Similarly, a difference between the temperature of the conditioningfluid leaving the first evaporator 110 via the outlet 218 and asaturated evaporating temperature of the first refrigerant 160 may beless than that of existing systems. As a result, a pressure of the firstrefrigerant 160 exiting the first evaporator 110, and therefore asuction pressure of the first refrigerant 160, may be greater than thatof existing systems, which enables a reduced energy consumption of thefirst compressor 104. In this way, operating costs of the HVAC&R system100 may be reduced. Indeed, while the average refrigerant and/orconditioning fluid temperatures of the first evaporator and secondevaporators 110 and 120 may be somewhat increased, an overall benefitand efficiency improvement of the HVAC&R system 100 may be realized withthe serial flow arrangement 150 described herein by virtue of theadvantages described above.

A further benefit of the serial flow arrangement 150 of the first andsecond evaporators 110 and 120 relates to manufacture of the HVAC&Rsystem 100. As mentioned above, the first evaporator 110 and the secondevaporator 120 have similar configurations and/or constructions and areconnected via the conduit 194. Thus, in some embodiments, a common orsingle design of a heat exchanger may be manufactured and mass producedfor use as each of the first evaporator 110 and the second evaporator120. Thus, costs of design and manufacture of the HVAC&R system 100 maybe reduced. Further, depending on desired configurations, packaging,and/or implementations of the HVAC&R system 100, positions of the firstevaporator 110 and the second evaporator 120 relative to one another maybe selected, and a suitable embodiment of the conduit 194 may becost-effectively manufactured or produced to enable fluid coupling ofthe first evaporator 110 and the second evaporator 120. Similarly,configurations and/or orientations of the inlets 170 and 196 and outlets192 and 218 may be readily selected or adjusted accordingly.

FIG. 5 is a top view of an embodiment of the first evaporator 110 andthe second evaporator 120 of the HVAC&R system 100 connected in theserial flow arrangement 150. Similarly, FIG. 6 is an axial view of theembodiment of the first evaporator 110 and the second evaporator 120shown in FIG. 5 . More specifically, the first evaporator 110 and thesecond evaporator 120 in the illustrated embodiments are positioned orarranged in side-by-side configuration (e.g., positioned such thatlengths of first evaporator 110 and the second evaporator 120 areadjacent or next to one another). The embodiments of FIGS. 5 and 6 havesimilar elements and element numbers as the embodiment of FIG. 4 and areconfigured to operate in a similar manner as that described above. Asdiscussed above, the serial flow arrangement 150 of the first evaporator110 and the second evaporator 120 enables conducive selection of arelative arrangement of the first evaporator 110 and the secondevaporator 120, while also providing a reduction in costs associatedwith manufacture and operation of the HVAC&R system 100. Indeed, thefirst and second evaporators 110 and 120 may have other configurationsrelative to one another in the serial flow arrangement 150, such as astacked configuration.

FIG. 7 is a schematic of an embodiment of the HVAC&R system 100 havingmultiple refrigerant circuits 34, including the first evaporator 110 andthe second evaporator 120 in the serial flow arrangement 150. Theillustrated embodiment also includes features that enable selectiveand/or adjustable control of the HVAC&R system 100. For example, theHVAC&R system 100 includes a controller 240 (e.g., control panel 44)having a memory 242 (e.g., non-volatile memory 50) and a processor 244(e.g., microprocessor 48). The controller 240 may be included with orseparate from the control panel 44. The memory 242 may be a mass storagedevice, a flash memory device, removable memory, or any othernon-transitory computer-readable medium that includes instructions forthe processor 244 to execute. The memory 242 may also include volatilememory such as randomly accessible memory (RAM) and/or non-volatilememory such as hard disc memory, flash memory, and/or other suitablememory formats. The processor 244 may execute the instructions stored inthe memory 242, in order to adjust operation of the HVAC&R system 100.

The controller 240 may be configured to control operation of componentsof the HVAC&R system 100, such as the components of the firstrefrigerant circuit 102 and the second refrigerant circuit 104 describedherein. In some embodiments, the controller 240 may adjust operation ofthe HVAC&R system 100 based on feedback received by the controller 240,such as feedback received from sensors 246 of the HVAC&R system 100. Oneor more of the sensors 246 may be configured to detect operatingparameters of the HVAC&R system 100, such as a temperature or pressureof the first refrigerant 160 circulated by the first refrigerant circuit102, a temperature or pressure of the second refrigerant 164 circulatedby the second refrigerant circuit 104, a temperature of the conditioningfluid, an operating mode of the HVAC&R system or a component thereof, anoperating load or capacity of the HVAC&R system, an ambient temperature,another suitable operating parameter, and/or any combination thereof.Further, one or more of the sensors 246 may be positioned at anydesirable location in order to detect an operating parameter, such asany desirable location along the first refrigerant circuit 102, thesecond refrigerant circuit 104, and/or the flow path of the conditioningfluid (e.g., the conditioning fluid circuit 124).

Based on the feedback received, the controller may adjust operation ofthe HVAC&R system 100. In some embodiments, operation of the first andsecond refrigerant circuits 102 and 104 may be adjusted based on anoperating load of the HVAC&R system 100. For example, when the HVAC&Rsystem 100 is operating at a 50 percent capacity, the first refrigerantcircuit 102 and the second refrigerant circuit 104 (e.g., thecompressors 104 and 114) may each be operated, via the controller 240,at 50 percent capacity. As another example, when the HVAC&R system 100is operating at 75 percent capacity, the first refrigerant circuit 102may be operated at 100 percent capacity, and the second refrigerantcircuit 104 may be operated at 25 percent capacity.

In some circumstances, the controller 240 may control operation of theHVAC&R system 100 such that one refrigerant circuit operates and theother refrigerant circuit does not operate. For example, at 25 percentcapacity of the HVAC&R system 100, the controller 240 may suspendoperation of the second refrigerant circuit 104 and may operate thefirst refrigerant circuit 102. To this end, the HVAC&R system 100 (e.g.,the conditioning fluid circuit 124) may include a bypass line configuredto route the conditioning fluid from the cooling load 122, through thefirst evaporator 110, and back to the cooling load 122, such that theflow of conditioning fluid bypasses the second evaporator 120. In theillustrated embodiment, a bypass valve (e.g., a three-way valve) 248 isdisposed along the conduit 194 and may be actuated (e.g., via thecontroller 240) to enable bypass of the second evaporator 120 and enableflow of the conditioning fluid from the cooling load 122 to the firstevaporator 110, as indicated by arrow 250.

Technical effects of the embodiments and features described aboveinclude improvements to operation and manufacture of HVAC&R systems(e.g., chillers) having multiple refrigerant circuits, such asimprovements in operating efficiency and cost reduction associated withoperation and manufacture of the HVAC&R systems. Specifically, theserial flow arrangement of the evaporators of multiple refrigerantcircuits enables a reduction in the evaporator approach temperature ofthe HVAC&R system. In this way, refrigerant pressure in the evaporatorsmay be raised, which may reduce a lift of the HVAC&R system andtherefore reduce the work performed by compressors of the HVAC&R system.Accordingly, energy consumption of the HVAC system is reduced.Additionally, the serial flow arrangement enables cost-effectivemanufacture of the HVAC&R system in multiple different structuralconfigurations or arrangements.

While only certain features of present embodiments have been illustratedand described herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be noted that the appendedclaims are intended to cover all such modifications and changes thatfall within the true spirit of the disclosure. Further, it should benoted that certain elements of the disclosed embodiments may be combinedor exchanged with one another.

The techniques presented and claimed herein are referenced and appliedto material objects and concrete examples of a practical nature thatdemonstrably improve the present technical field and, as such, are notabstract, intangible or purely theoretical. Further, if any claimsappended to the end of this specification contain one or more elementsdesignated as “means for [perform]ing [a function] . . . ” or “step for[perform]ing [a function] . . . ”, it is intended that such elements areto be interpreted under 35 U.S.C. 112(f). However, for any claimscontaining elements designated in any other manner, it is intended thatsuch elements are not to be interpreted under 35 U.S.C. 112(f).

1. A heating, ventilation, air conditioning, and/or refrigeration(HVAC&R) system, comprising: a first refrigerant circuit comprising afirst evaporator configured to place a first refrigerant in a heatexchange relationship with a conditioning fluid, wherein the firstevaporator comprises a first set of first tubes and a second set offirst tubes configured to direct the conditioning fluid through thefirst evaporator; a second refrigerant circuit comprising a secondevaporator configured to place a second refrigerant in a heat exchangerelationship with the conditioning fluid, wherein the second evaporatorcomprises a first set of second tubes and a second set of second tubesconfigured to direct the conditioning fluid through the secondevaporator; and a conditioning fluid circuit configured to circulate theconditioning fluid serially through the first set of first tubes, thesecond set of first tubes, the first set of second tubes, and the secondset of second tubes.
 2. The HVAC&R system of claim 1, wherein the firstset of first tubes defines a lower pass of the first evaporator, and thesecond set of first tubes defines an upper pass of the first evaporator.3. The HVAC&R system of claim 2, wherein the first evaporator comprisesa water box configured to receive the conditioning fluid from the firstset of first tubes, reverse a flow direction of the conditioning fluidthrough the first evaporator, and direct the conditioning fluid into thesecond set of first tubes.
 4. The HVAC&R system of claim 2, wherein thefirst set of second tubes defines a lower pass of the second evaporator,and the second set of second tubes defines an upper pass of the secondevaporator.
 5. The HVAC&R system of claim 4, wherein the conditioningfluid circuit comprises a conduit extending from an outlet of the secondevaporator to an inlet of the first evaporator, the outlet of the secondevaporator is configured to direct the conditioning fluid from thesecond set of second tubes toward the conduit, and the inlet of thefirst evaporator is configured to direct the conditioning fluid from theconduit toward the first set of first tubes.
 6. The HVAC&R system ofclaim 1, wherein the first evaporator comprises an outlet, the secondevaporator comprises an inlet, the outlet is configured to direct theconditioning fluid toward a cooling load, and the inlet is configured toreceive the conditioning fluid from the cooling load.
 7. The HVAC&Rsystem of claim 1, wherein the first evaporator and the secondevaporator are arranged in an end-to-end configuration relative to oneanother.
 8. The HVAC&R system of claim 1, wherein the first evaporatorand the second evaporator are arranged in a side-by-side configurationrelative to one another.
 9. The HVAC&R system of claim 1, comprising achiller having the first refrigerant circuit and the second refrigerantcircuit, wherein the first refrigerant circuit comprises a firstcondenser configured to place the first refrigerant in a heat exchangerelationship with ambient air, and the second refrigerant circuitcomprises a second condenser configured to place the second refrigerantin a heat exchange relationship with ambient air.
 10. A heating,ventilation, air conditioning, and/or refrigeration (HVAC&R) system,comprising: a first evaporator comprising a first lower tube bundle anda first upper tube bundle, wherein the first lower tube bundle and thefirst upper tube bundle are each configured to place a conditioningfluid in a heat exchange relationship with a first refrigerant; a secondevaporator comprising a second lower tube bundle and a second upper tubebundle, wherein the second lower tube bundle and the second upper tubebundle are each configured to place the conditioning fluid in a heatexchange relationship with a second refrigerant; a conduit fluidlyextending between the first evaporator and the second evaporator andfluidly coupling the first lower tube bundle and the second upper tubebundle; and a conditioning fluid circuit configured to circulate theconditioning fluid serially through the second lower tube bundle, thesecond upper tube bundle, the conduit, the first lower tube bundle, andthe first upper tube bundle.
 11. The HVAC&R system of claim 10, whereinthe conditioning fluid circuit is configured to direct the conditioningfluid from a cooling load to the second lower tube bundle and from thefirst upper tube bundle to the cooling load.
 12. The HVAC&R system ofclaim 10, wherein the first lower tube bundle defines a first pass ofthe first evaporator, and the first upper tube bundle defines a secondpass of the first evaporator.
 13. The HVAC&R system of claim 12, whereinthe second lower tube bundle defines a first pass of the secondevaporator, and the second upper tube bundle defines a second pass ofthe second evaporator.
 14. The HVAC&R system of claim 10, comprising: afirst refrigerant circuit comprising the first evaporator, a firstcompressor, and a first condenser, wherein the first condenser isconfigured to place the first refrigerant in a heat exchangerelationship with ambient air; and a second refrigerant circuitcomprising the second evaporator, a second compressor, and a secondcondenser, wherein the second condenser is configured to place thesecond refrigerant in a heat exchange relationship with ambient air,wherein the first refrigerant circuit and the second refrigerant circuitare fluidly separate from one another.
 15. A chiller system, comprising:a first refrigerant circuit comprising a first evaporator configured toplace a first refrigerant in a heat exchange relationship with aconditioning fluid, wherein the first evaporator comprises a firstplurality of first tubes and a second plurality of first tubesconfigured to direct the conditioning fluid through the firstevaporator, wherein the first plurality of first tubes defines a lowerpass of the first evaporator, and the second plurality of first tubesdefines an upper pass of the first evaporator; a second refrigerantcircuit comprising a second evaporator configured to place a secondrefrigerant in a heat exchange relationship with the conditioning fluid,wherein the second evaporator comprises a first plurality of secondtubes and a second plurality of second tubes configured to direct theconditioning fluid through the second evaporator, wherein the firstplurality of second tubes defines a lower pass of the second evaporator,and the second plurality of second tubes defines an upper pass of thesecond evaporator; and a conduit extending between and fluidly couplingthe second plurality of second tubes and the first plurality of firsttubes.
 16. The chiller system of claim 15, wherein the first evaporator,the second evaporator, and the conduit are configured to direct theconditioning fluid serially through the second plurality of secondtubes, the first plurality of second tubes, the conduit, the firstplurality of first tubes, and the second plurality of first tubes. 17.The chiller system of claim 15, wherein the first refrigerant circuitcomprises a first air-cooled condenser, the second refrigerant circuitcomprises a second air-cooled condenser, and the first refrigerantcircuit and the second refrigerant circuit are fluidly separate from oneanother.
 18. The chiller system of claim 15, wherein the firstevaporator and the second evaporator are positioned in an end-to-endarrangement relative to one another.
 19. The chiller system of claim 15,wherein the first evaporator and the second evaporator are positioned ina side-by-side arrangement relative to one another.
 20. The chillersystem of claim 15, comprising a controller configured to regulateoperation of the first refrigerant circuit and the second refrigerantcircuit independently of one another based on feedback received from oneor more sensors of the chiller system.